This invention relates to an internal combustion engine and more particularly to an improved cam shaft drive for such engines employing a variable valve timing mechanism.
In order to improve the flexibility of internal combustion engines and to provide a more desirable power curve, it has been proposed to employ a variable valve timing mechanism. By varying the phase angle of one or both cam shafts, it is possible to obtain optimum valve events for most running conditions of the engine.
The conventional type of variable valve timing mechanism (VVT) is normally positioned in the connection between a driving element mounted on the cam shaft and the cam shaft itself. These VVT mechanisms employ a hydraulically operated mechanism that shifts the phase angle of the cam shaft from its driving element, normally a sprocket.
Although the use of variable valve timing mechanisms has considerable advantages, the placement of the variable valve timing mechanism at the driving connection between the cam shaft and its driving element has some disadvantages. First, the variable valve timing mechanism has a fairly substantial size and thus, the overall length of the engine is generally increased through the use of VVT mechanisms. Also, when the mechanism is disposed in cantilevered fashion at the outward end of the cam shaft, there can be relatively high bending loads exerted on the cam shaft and heavy wear in the adjacent cam shaft bearing may result.
Also, the variable valve timing mechanisms are normally powered by the lubricant from the lubricating system of the engine. At times, this can present some problems in the delivery and return of the lubricating oil to and from the VVT mechanism.
It is, therefore, a principal object of this invention to provide an improved cam shaft driving arrangement for an engine.
It is a further object of this invention to provide an engine cam shaft driving arrangement wherein the cam shaft is driven by a variable valve timing mechanism that is not mounted at the end of the controlled cam shaft.
It is a further object of this invention to provide a variable valve timing mechanism that is interposed in the cam shaft driven in such a way as to minimize the size added to the engine.